Apparatus for the induction heating of metal sheets and process for heating such metal sheets

ABSTRACT

An apparatus for the induction heating of metal sheets. The apparatus comprises generally an alternating current generator, an inductor connected to the generator, and a guideway for the metal sheets to be heated passing through the inductor in a direction such that the lines of force of the magnetic field are parallel to the guideway and to themselves inside the guideway. The inductor is made in the form of a curved loop having two arms and surrounding the guideway. The loop consists of at least one main portion in which the area located between the two arms is crossed by the guideway and at least two secondary portions which are parallel to the lateral edges of the guideway and run along such lateral edges at a predetermined distance therefrom. The process for carrying out the heating of the metal sheets consists in passing the sheets inside the guideway through the inductor.

0 United States Patent 11 1 1111 33%,353 Barhieux 1 Get. 16, 197 3 [5 APPARATUS FOR THE INDUCTION 3,058,840 l0/l962 Kerr et al...., 219/10.61 x HEATING 0F METAL SHEETS AND 3,444,346 5/1969 Russell et al i 1 219/10.61 PROCESS FOR HEATING SUCH METAL 3,301,991 l/1967 Geisel 219/10.69 X

SHEETS Inventor: Andre Barbieux, Rue

Foreign Application Priority Data Jan. 15, 1972 Belgium 98 609 US. Cl 219/10.61, 2l9/l0.67, 219/1079 Int. Cl. H051) 5/08 Field of Search 2l9/l0.6l, 10.69,

2l9/lO.79, 10.67, 10.71, 10.43

References Cited UNITED STATES PATENTS 9/1970 Viart 219/1041 X Primary ExaminerBruce A. Reynolds Attorney-Raymond A. Robic [5 7] ABSTRACT An apparatus for the induction heating of metal sheets. The apparatus comprises generally an alternating current generator, an inductor connected to the generator, and a guideway for the metal sheets to be heated passing through the inductor in a direction such that the lines of force of the magnetic field are parallel to the guideway and to themselves inside the guideway. The inductor is made in the form of a curved loop having two arms and surrounding the guideway. The loop consists of at least one main portion in which the area located between the two arms is crossed by the guideway and at least two secondary portions which are parallel to the lateral edges of the guideway and run along such lateral edges at a predetermined distance therefrom. The process for carrying out the heating of the metal sheets consists in passing the sheets inside the guideway through the inductor.

2 Claims, 4 Drawing Figures #AIENIEM 15 ms sum 1 or 2 FIG.

This invention relates to an apparatus for the induction heating of metal sheets which permits to reach a temperature which is perfectly uniform across the whole-section of the metal sheets and to a process for carrying out heating of the metal sheets.

It is already known to heat metal sheets in an apparatus in which an alternating current generator of low, medium or high frequency feeds an inductor crossed by a guideway for the metal sheets to be heated. In such an apparatus, the direction of the lines of force of the magnetic field of the inductor is parallel to the guideway, and inside the guideway, the lines of force are parallel to themselves. This known apparatus does not permit to obtain a temperature which is perfectly uniform across the whole section of the metal sheets because the edges of the sheets are always warmer. The excessive heating of the lateral edges of the sheets is particularly cumbersome when the metal sheets are made of magnetic material and if the final temperature must stay below the Curie point. In certain cases, it has been possible to overcome such difficulty by heating the metal sheets up to a temperature above the Curie point and by subsequently cooling the metal sheets down to the desired temperature. This simple process has not always been applicable because either the superficial surface of the metal sheets or the total compositionof the sheets may undergo nonreversible modifications (oxydation, increase in size of the grains, etc.) when the temperature exceeds a predetermined threshold value.

The invention permits to prevent the overheating of the lateral edges of the metal sheets and to obtain a heating at a temperature perfectly uniform across the whole section of the metal sheets. It is characterized in that the inductor consists of a curved loop surrounding a guideway for the metal sheets and composed of at least one main portion in which the area located between the two arms of the loop is crossed by the guideway and of two secondary portions placed on each side of the main portion which extend in a direction parallel to the lateral edges of the guideway and at a predetermined distance from such lateral edges, When the inductor comprises two main portions, the loop may be bent in a rectangular shape and if the number of the main portions is higher, the loop is bent in a zigzag form.

The invention also concerns a process for heating metal sheets. Such process is characterized in that the metal sheets are passed through the guideway and thus through one or plural inductors as disclosed above and in that the distance between the lateral edges of the metal sheets and the secondary portions of the inductor is adjusted at a predetermined value.

The invention will now be disclosed with respect to three schematic embodiments'thereof and to a practical embodiment and with respect to the attached drawings in which:

FIG. 1 illustrates a perspective view of a schematic embodiment of an apparatus in accordance with the invention;

FIG. 2 illustrates a plan view of another schematic embodiment of an apparatus in accordance with the invention;

FIG. 3 illustrates a perspective view of another schematic embodiment of the invention; and

FIG. 4 illustrates a perspective view, partially in cross-section of an apparatus permitting to realize the schematic embodiment of FIG. 3.

Referring to FIG. 1, an alternating current generator 1 feeds an inductor having two arms 2, 2', 2" and 3, 3', 3" having the form of a curved loop similar to a hair pin. Such inductor is composed of a main portion 2, 3 and of two secondary portions 2', 3', and 2", 3". The area located between the two arms 2, 3 of the main portion is crossed by a guideway 4 for the sheet metals to be heated. The secondary portions extend parallel to the lateral edges of the guideway 4 at a predetermined distance therefrom.

In FIG. 2, the generator 1 also feeds an inductor having two arms but only one of the arms is visible because FIG. 2 is a plan view. Such inductor also has the shape of a curved loop, but instead of being bent in the shape of a C, such as the inductor of FIG. 1, the inductor according to FIG. 2 is bent in a zigzag form made of portions 5 to 13. The portions 6, 8, 10 and 12 are the main portions which cross the guideway 4 whereas the portions 5, 7, 9, l1 and 13 are the secondary portions which run along the lateral edges of the guideway 4.

FIG. 3 illustrates schematically an inductor made of an upper arm 15 to 23 and of a lower arm 24 to 32. Such inductor comprises two main portions composed of parts 16, 17, 18 and 29, 30, 31 on the one hand and of parts 20, 21, 22 and 25, 26, 27 on the other hand. The inductor also comprises three secondary portions formed by the parts 15, 32; 19, 28 and 23, 24 of the arms. The main portions are each madeof a central part 17, 30 and 21, 26 and of two end parts 16, 31 18, 29; 27, 33 and 22, 25. The central parts of the main portions are placed facing the central part of the guideway 4 of the metal sheets. The end parts of the main portions are located facing the lateral edges of the guideway 4. The parts of the upper and lower arms forming the end parts of the main portions are located at a distance which is relatively large with respect to each other. Such distance is lower for the parts of the arms forming the central parts of the main portions and still lower for the parts of the arms forming the secondary portions. This arrangement produces the following effects; the stray field of the secondary portions is located in a space closely surrounding the secondary portions. The inductive coupling is very loose at the location of the lateral edges of the metal sheets to be heated and is much stronger at the location of the centra part of the metal sheets. The current flows from the secondary portions of the inductor to the end parts of the main portions and vice versa by means of inclined parts 33 of the arms of the inductor and from the end parts to the central parts of the main portions of the inductor and vice versa by means of inclined parts 34. In order to equalize the repartition of the current in the main portions, the width of the main portions is narrowed down at the end parts thereof by means of cutout parts 35.

FIG. 4 illustrates a portion of a practical embodiment of the inductor shown in FIG. 3. FIG. 4 illustrates the end parts 18, 29 of FIG. 3. A frame made of copper sheet 36 is placed facing another frame of copper sheet 37. Each of the frames 36 and 37 is cooled by means of a water conduit 38. To the frame 36 is secured a copper flat plate 39 and a copper flat plate 46. To the frame 37 is secured a copper flat plate 41 and a copper flat plate 42. The two flat plates 40 and 42 are separated by a thin insulator 43 and are thicker than flat plates 39 and 41. The flat plates 39 and 41 are placed facing the central part of the guideway 4. The lower surface of flat plate 39 corresponds to the portion 17 of FIG. 3. The free lower surface of frame 36 corresponds to portion 18 and the lower surface of flat plate 40 in contact with the insulator corresponds to portion 19 of FIG. 3. In place of the cutout portions 35 of FIG. 3, slots 44 are cut into frames 36 and 37. If, at predetermined locations, it is desired to modify the strength of the heating, it is possible to make holes 45 in the frames 36 or 37 and through the flat plates 39 or 41. Since the frames are fed by currents at high frequency, the skin effect will occur. Consequently, the current will flow at the opposed surfaces of the frames so that the embodiment of FIG. 4is perfectly equivalent to the arrangement illustrated in-FIG. 3.

In FIGS. 1 to 4, the guideway for the metal sheets is illustrated as being located in a plane. It is obvious that the metal sheets could also move themselves in a curved guideway and that, in' this case, the frames 36 and 37 would follow the curvature of such guideway. The heating apparatus may comprise not only an alternating current generator but plural generators feeding each an inductor in accordance with the invention. The frequency of the alternating current ischosen in function of the desired depth of penetration of the currents induced in the metal sheets. For thin metal sheets, such frequency is thus chosen 'in the radio frequencies. In the guideway, the metalsheets may be moved either in a continuous way if the full surface of the metal sheets is to be heated,'or step by step if certain portions of the metal sheets only are to be heated.

If a metal sheet is to be completely heated, the sheet is passed in a continuous way through one or plural inductors such as disclosed above. The temperature of the metal sheet is measured at the output of the inductors. Such temperature is compared with a reference temperature and the strength of the current and/or the speed of movement of thesheet is controlled to reduce to zero the difference between the measured tempera ture and thevreference temperature.

-I claim: I

1. Apparatus for the induction heating of metal sheets comprising an alternating current generator, an inductor connected to said generator, a guideway for a metal sheet to be heatedpassing through said inductor in a direction such that the lines of force of the magnetic field are parallel to the guideway and to themselves inside said guideway, characterized in that the inductor comprises a curved loop having two arms and surrounding said guideway, said loop consisting of at least one main portion in which the area located between said two arms is crossed by the guideway; at least two secondary portions which are parallel to the lateral edges of said guideway and run along said lateral edges at a predetermined distance therefrom; one said secondary portion being adjacent to each extremity of each said main portion; and the main portion of the inductor consisting of flat strips of metal of which the flat strip sides face the guideway, each said flat strip having a median part shorter than the breadth of the guideway disposed close to the guideway and end parts bent to a greater distance from the guideway and connected to said secondary portions.

2. Apparatus for the induction heating of metal sheets comprising an alternating current generator, an inductor connected to said generator, a guideway for a metal sheet to be heated passing through said inductor in a direction such that thelines of force of the magnetic field are parallel to the guideway and to themselves inside said guideway, characterized in that the inductor comprises a curved loop having two arms and surrounding said guideway, said loop consisting of at least one main portion in which the area'located between said two arms is crossed by the guidewaytat' least two secondary portions which are parallel to' the lateral edges of said guideway and run along said lateral edges at a predetermined distance therefrom; one said secondary portion being adjacent to each extremity of each said main portion; and the main portion of the inductor consisting of flat strips of metal of which the flat sides face the guideway, said flat strips being disposed in parallel planes and having metalbars shorter than the breadth of the guideway fixed on a median part of each strip on the sides of the strips facing the guideway, the extremities of said flap strips being connected to said secondary portions. 

1. Apparatus for the induction heating of metal sheets comprising an alternating current generator, an inductor connected to said generator, a guideway for a metal sheet to be heated passing through said inductor in a direction such that the lines of force of the magnetic field are parallel to the guideway and to themselves inside said guideway, characterized in that the inductor comprises a curved loop having two arms and surrounding said guideway, said loop consisting of at least one main portion in which the area located between said two arms is crossed by the guideway; at least two secondary portions which are parallel to the lateral edges of said guideway and run along said lateral edges at a predetermined distance therefrom; one said secondary portion being adjacent to each extremity of each said main portion; and the main portion of the inductor consisting of flat strips of metal of which the flat strip sides face the guideway, each said flat strip having a median part shorter than the breadth of the guideway disposed close to the guideway and end parts bent to a greater distance from the guideway and connected to said secondary portions.
 2. Apparatus for the induction heating of metal sheets comprising an alternating current generator, an inductor connected to said generator, a guideway for a metal sheet to be heated passing through said inductor in a direction such that the lines of force of the magnetic field are parallel to the guideway and to themselves inside said guideway, characterized in that the inductor comprises a curved loop having two arms and surrounding said guideway, said loop consisting of at least one main portion in which the area located between said two arms is crossed by the guideway; at least two secondary portions which are parallel to the lateral edges of said guideway and run along said lateral edges at a predetermined distance therefrom; one said secondary portion being adjacent to each extremity of each said main portion; and the main portion of the inductor consisting of flat strips of metal of which the flat sides face the guideway, said flat strips being disposed in parallel planes and having metal bars shorter than the breadth of the guideway fixed on a median part of each strip on the sides of the strips facing the guideway, the extremities of said flap strips being connected to said secondary portions. 